Add support for additional file formats (CSV, XML, YAML)

[anitnilay20]

Description

Building on the FileViewer architecture established in the recent refactoring, add support for viewing additional file formats beyond JSON/NDJSON.

Background

The codebase has been refactored to separate generic file viewing logic (FileViewer) from format-specific rendering (JsonTreeViewer). This architecture makes it straightforward to add new file format viewers.

Proposed File Formats

Priority 1 - High Value

• CSV/TSV - Tabular data display with column headers, sorting, filtering
• XML - Tree-based viewer similar to JSON, with attribute support
• YAML - Tree viewer with YAML-specific syntax handling

Priority 2 - Nice to Have

• TOML - Config file support
• Plain Text - Basic text viewer with syntax highlighting
• Markdown - Rendered preview

Implementation Plan

Each format viewer should:

1. Implement a dedicated viewer (e.g., CsvTableViewer, XmlTreeViewer)
2. Integrate with FileViewer via format detection
3. Support common operations: search, copy, export
4. Maintain consistent UI/UX with existing JSON viewer

Technical Notes

Current architecture:

• FileViewer (generic parent) - handles loading, caching, selection
• JsonTreeViewer (JSON-specific) - renders JSON tree structure
• ViewerState (shared) - common state across viewers

New viewers should follow this pattern and reuse the existing infrastructure.

Related Issues

• Closes Modularize JsonViewer - separate rendering, state, and caching concerns #19 (Modularize JsonViewer) ✅
• Related to Refactor file module - split lazy_loader.rs into separate components #18 (Refactor file module)

Acceptance Criteria

• CSV/TSV files display in tabular format
• XML files display in tree structure
• YAML files display in tree structure
• File type auto-detection works correctly
• Search functionality works across all formats
• Performance remains good for large files (lazy loading where applicable)
• All keyboard shortcuts work consistently